The invention relates to a fuel injection system for mixture compressing internal combustion engines which employ continuous fuel injection into the induction manifold. The induction manifold includes an air flow sensor and an arbitrarily settable throttle plate. The air flow sensor is displaced by the flowing air and is returned to its normal position by a restoring force and, during its motions, displaces the control plunger of a fuel metering and distributing system which apportions fuel to the air.
Fuel injection systems of this type have the purpose to provide automatically a favorable fuel-air mixture for all operational conditions of the engine so as to insure complete combustion and the highest power or least fuel consumption. At the same time, the generation of toxic exhaust gas constituents is intended to be sharply reduced. For these purposes, it is required that the fuel quantity be metered out very precisely.
In known fuel injection systems of this type, it is a design criterion to meter out the fuel as nearly as possible proportional to the air mass flowing through the induction tube and the ratio of air to fuel may be altered by changing the restoring force of the air flow sensor in dependence on certain operational variables of the engine and by means of at least one pressure control valve.
In order to insure proper starting of engines at temperatures lower than approximately 20.degree. C., the known fuel injection systems are provided with a starting mechanism which includes mainly an electromagnetic starting valve which is energized together with the engine starter and which also has a thermal time switch which limits the opening time of the magnetic valve and completely inhibits it at certain higher temperatures. The electromagnetic starting valve injects the supplementary fuel into the common induction manifold. The thermal time switch opens and closes the electrical circuit of the valve in dependence on engine temperature. When engine starting takes place at a temperature less than +20.degree. C., an electrically heated bimetallic spring eventually interrupts the electric circuit.
A cold starting mechanism of this type not only requires a considerable additional expense because of the presence of the additional electromagnetic valve and the thermal switch but, in addition, the injection of fuel into the common manifold produces rather poor fuel distribution with respect to the individual cylinders.